Stable tuning device for high-frequency radio circuits



Feb. 5, 1946. c. T. MARTowlcz 2,394,391

STABLE TUNING DEVICE FOR HIGH FREQUENCY RADIO CIRCUITS Filed July 22,1944 Q\ ZOZ N` y 5 m N Y N i N \\LF X\ X\\\ INVENTOR.V

CHESTER T. MARToWIcz H15 A'rro NzyS- Patented Feb. 5, 1946 STABLE TUNINGDEVICE FOR HIGHl-FRE- QUENCY RADIO CIRCUITS QhesterT. Martowicz, NewYork, N. Y.,. assigner, byl mesne assignments, to Henry L. Crowley,

South Orange. N. J.

Application July 22, 1944, Serial No. 546,109

(Cl. Z50-40) 3 Claims.

This invention relates to a simple apparatus for providing an increasedand specialized frequency range for permeability tuning circuits.

The primary object of this invention is to provide an inductor and acapacitor in a gang combination of which each unit is capable ofvariation in electrical properties.

Another object of this invention is to provide such a gang device toafford a completely stable tuning circuit for high frequency radiopurposes which is adaptable to adjustment for a wide range offrequencies.

This invention resides substantially in the combination of parts asherein disclosed.

In the accompanying drawing,

Figure l is a cylindrical. cross-sectional view somewhat in diagrammaticform of a gang inductor-cenacitor tuning device in accordance with thisinvention; and

Figure 2 is a diagrammatic circuit illustration of the device oi Figure1.

It is general practice to tune radio circuits by the use of a xedinductor and a variable capacltor. This method. however. possesses thedisadvantage of thermal instability among others. Some radio circuitshave been designed using a variable inductor with a xed capacitancegenerally furnished by the circuit itself. However, this arrangement isunsatisfactory primarily because of the limited tuning range soobtained. In accordance with this invention the variable inductorcapacitor possesses a tuning range of 1.7 to 1 at high frequencies andan even larger tuning range at the lower broadcast frequencies (3.6 tol) The objects and advantages of this invention will be apparent bydetailed reference tothe structure illustrated in the drawing. Thedevice consists of an inculating coil form made of some suitablematerial determined in part by the frequency range in which the deviceis to be used. For high frequency purposes this coil form I ispreferably made of a Steatite ceramic formed with a central passagetherethrough as shown and provided with a series of peripheral grooves.Proceeding from right to left the iirst groove is of larger axial extentand has mounted therein a single interrupted or incomplete turn I I ofsome suitable metal such as silver or copper. The other groove is ofhelical form made by a series of helical turns each of which has asmaller axial extent than the iirst groove referred to. Mounted in thishelical groove is a conductor in the form of a thin strip I2 of somesuitable metal. This strip is open at the ends and has the adjacent endconnected to the against that of the coil components.

incomplete turn II by means of the conducting jumper I3.

The conductors I I and I2 may be formed in the grooves by depositing athin coat of silver or other metal therein, or in any other suitablemanner. The chamber I3 is diagrammatically illustrated and it isapparent that this connection can be made in a number of diierent ways,and may for example be embedded in the coil form I0.

The far end of the conductor I2 is connected by the lead I4 whichlikewise could be embedded in the coil form to a metal plate I8 mountedon the end of the coil form. Threadedly mounted in this plate is alongitudinal adjustable screw I9 which extends` into the coil form andis mechanically and electrically connected to a movable cup comprisingthe ncnferrous portion I 5 such as copper, for example, and the magneticportion I6 such as soft iron. The two core portions are mechanically andelectrically united together as shown at Il.

As` a feature of relative unimportance it is noted that the freeunsupported end of the core may be provided with some sort of guidingmeans to guide it centrally of the conductors II and I2. A permanentconnection 20 is electrically connected to the conductor I2, as shown,and provides one terminal for the circuit combination formed by thedevice. The other terminal is provided by the lug 2| and the plate I8. f

Figure 2 diagrammatically illustrates the circuit resulting from thiscombination of parts. The same reference numerals have been used on therespective parts so that the circuit provided by the device is clearfrom Figure 2.

As previously noted while the coil form I 0 is preferably made ofSteatite for use at high frequency, or some equivalent material, otherinsulating materials are available for use especially at lowerfrequencies, as for example many of the plastic materials now common inthe electrical arts.

When the Steatite coil form is employedthe de vice may be readilydesigned with a minimum of diiilculty for a maximum of stability bybalancing the temperature coeflicient of the coil form The magnetic coreI6 is preferably made of powdered iron under pressure and sintered inaccordance with well known practice in the art to provide a powderediron core especially suitable for high frequency operations. Steatitecoil forms can be readily constructed with a thermo drift as low as sixparts per million per degree centigrade, and

can be balanced against the thermo drift of high p frequency powderediron cores as loW as two parts per million per degree centigrade. Thethermo drift refers to the change in electrical properties of thesedevices with temperature changes. The effect on the electricalproperties of the device by the thermo drift of the powdered core can bebalancedby the thermo drift in an opposite sense and the Steatite coilform with temperature changes resulting in a minimization of the overallchange in electrical properties of the device.

It will be apparent, a5 illustrated in Figure 1. that the inductance andthe capacity of the device are at a maximum and that as the core isadjusted to the left by the screw i9 these forms may be correctly andscientifically brought to a minimum Value.

From the above description it will be apparent to those skilled in theart that the subject matter of this invention is capable of considerablevariation, and I do not, therefore, desire to be limited to thedisclosure as given in an illustrative sense, but rather to the claimsgranted me.

What is claimed is:

1. A gang inductor-capacitor comprising an insulating support ofSteatite having a passage therethrough, a condenser plate and aninducta-nce winding surrounding said support, means for electricallyconnecting the plate to one terminal of said Winding, a movable corelying in said passage composed of a ferrous and a nonferrous portionlying between said inductance winding and condenser plate respectively,a Connection between the other end of the Winding and said core, andmeans for longitudinally positioning said core.

2. In the combination of claim 1, said condenser plate comprising anincomplete turn on said form.

3. In the combination of claim 1, said condenser plate comprising anincomplete turn and said inductance winding comprising a plurality ofhelical turns.

CHESTER T. MARTOWICZ.

